<div class="demo">
  test01 演示类的继承
  默认情况下，类的所有成员都是public

  <div class="demo">
    varRoot:{{varRoot.name}}
  </div>
  <div class="demo">
    varA: {{varA.name}},
  </div>
  <div class="demo">
    <button (click)="addB()">add data</button>
    varB:{{varB.len()}}
  </div>

</div>
